The invention relates to an electrode for electrolytic processes, in particular to a cathode suitable for hydrogen evolution in an industrial electrolytic process. The electrolysis of alkali brines for the simultaneous production of chlorine and alkali and the electrochemical processes of hypochlorite and chlorate manufacturing are the most typical examples of industrial electrolytic applications where hydrogen is cathodically evolved, but the electrode is not limited to any particular application. In the industry of electrolytic processes, competitiveness depends on several factors, and primarily on the reduction of energy consumption, which is directly associated with the operating voltage. This is the main reason behind the efforts directed to reduce the various components making up the cell voltage, cathodic overvoltage being one of those. Cathodic overvoltages which can be naturally obtained with electrodes of chemically-resistant materials (for instance carbon steel) free of catalytic activation were considered acceptable for a long time. The market nevertheless increasingly requires, for this specific technology, a caustic product of high concentration, making the use of carbon steel cathodes unviable due to corrosion problems. Moreover, the increase in the cost of energy has made the use of catalysts facilitating the cathodic evolution of hydrogen economically more convenient. One possible solution is the use of nickel substrates, chemically more resistant than carbon steel, coupled with platinum-based catalytic coatings. Cathodes of such kind are normally characterised by acceptably reduced cathode overvoltages, resulting rather expensive due to their content of platinum and to their limited operative lifetime, probably caused by the poor adhesion of the coating to the substrate. A partial improvement in the adhesion of catalytic coatings on nickel substrates can be obtained by adding cerium to the formulation of the catalytic layer, optionally as an external porous layer aimed at protecting the underlying platinum-based catalytic layer. However, this type of cathode is prone to suffer considerable damages following the occasional current reversals inevitably taking place in the case of malfunctioning of industrial plants.
A partial improvement in the current reversal tolerance is obtainable by activating the nickel cathodic substrate with a coating consisting of two distinct phases, a first phase containing the noble metal-based catalyst and a second phase comprising palladium, optionally in admixture with silver, having a protective function. This kind of electrode presents, however, a sufficient catalytic activity only when the noble metal phase contains high amounts of platinum, preferably with a significant addition of rhodium. Replacing platinum with cheaper ruthenium in the catalytic phase entails, for example, the onset of considerably higher cathodic overvoltages. Furthermore, the preparation of the coating consisting of two distinct phases requires an extremely delicate process control to achieve sufficiently reproducible results.
There is then a need for providing a new cathode composition for industrial electrolytic processes, in particular for electrolytic processes with cathodic evolution of hydrogen, characterised, with respect to prior art formulations, by an equivalent or higher catalytic activity, a lower overall cost in terms of raw materials, a higher reproducibility of preparation, and a lifetime and tolerance to accidental current reversal equivalent or higher in the usual operative conditions.